Surgical communication and power system

ABSTRACT

An apparatus for determining the position of a wireless catheter probe being used during a surgical procedure. Magnetic fields are projected into an anatomical body to induce voltage signals in a sensing coil that are sufficient to describe the position of a wireless sensor/transmitter. The voltage signals are wirelessly re-transmitted by the sensor/transmitter as positional signals indicative of a current location of the sensor/transmitter in the anatomical body. In a preferred embodiment, the wireless catheter probe is self-powered using the induced voltage signals on a sensing coil. In another embodiment, induced voltage signals of a separate coil are used to power the device.

CONCURRENTLY FILED APPLICATIONS

The following United States patent applications, which were concurrentlyfiled with this one on Oct. 28, 1999, are fully incorporated herein byreference: Method and System for Navigating a Catheter Probe in thePresence of Field-influencing Objects, by Michael Martinelli, PaulKessman and Brad Jascob; Patient-shielding and Coil System, by MichaelMartinelli, Paul Kessman and Brad Jascob; Navigation Information Overlayonto Ultrasound Imagery, by Paul Kessman, Troy Holsing and JasonTrobaugh; Coil Structures and Methods for Generating Magnetic Fields, byBrad Jascob, Paul Kessman and Michael Martinelli; Registration of HumanAnatomy Integrated for Electromagnetic Localization, by Mark W. Hunterand Paul Kessman; System for Translation of Electromagnetic and OpticalLocalization Systems, by Mark W. Hunter and Paul Kessman; and SurgicalSensor, by Mark W. Hunter, Sheri McCoid and Paul Kessman.

BACKGROUND OF THE INVENTION

A. Field of the Invention

The present invention relates to wireless remote medical devices. Theinvention has particular application when used with a method and systemfor determining the position of a wireless catheter probe being usedduring a surgical procedure.

B. Description of the Related Art

Various locating systems have been used in the past to determine theposition of an object such as the tip of an endoscope or a catheterwithin the human body.

Systems and methods are known for determining the location of a catheteror endoscopic probe inserted into a selected body cavity of a patientundergoing a surgical procedure. For example, there exist systems thatmay use acoustics, optics, conductance and electromagnetics to locate or“localize” a medical instrument in an anatomical body. In anelectromagnetic system, location data may be obtained from electricalmeasurements of voltage signals that are induced within a sensing coilaffixed to the distal end of the catheter prove. A voltage is induced inthe sensing coil in response to pre-specified electromagnetic fieldsthat project into the anatomical region of interest which contains allprospective locations of the catheter probe. The electrical measurementsof the induced signals may provide sufficient information to compute theangular orientation and the positional coordinates of a coil in asensor, and hence the catheter probe, which collectively define thelocation of the coil.

Regardless of the technical particulars of a surgical localizationsystem, each system typically includes a component internal to thepatient associated with a medical device and a component external to thepatient for calculating the position of the medical instrument.

SUMMARY OF THE INVENTION

The present invention is directed to improving communication linksbetween internal and external surgical navigation components and toproviding wireless power to internal components.

The invention in its broadest sense may include one or more of thefollowing aspects alone or in combination with one or more elements:

an apparatus and method for locating a wireless sensor/transmitterwithin an anatomical body,

at least one signal generator for sending reference signals through theanatomical body to be received by the sensor/transmitter and to bewirelessly re-transmitted by the sensor/transmitter as positionalsignals indicative of a current location of the sensor/transmitter inthe anatomical body,

a receiver for receiving positional signals from the wirelesssensor/transmitter,

a processor for computing a position of a wireless sensor/transmitter asa function of the positional signals transmitted to a receiver, and acircuit associated with the processor for outputting position imageinformation to a display device,

a wireless sensor/transmitter for use in surgical procedures to trackthe movement of structures within an anatomical body having a portionfor receiving a reference signal from a reference signal generator, anda portion for wirelessly transmitting the reference signal as apositional signal indicative of a current position of the sensor andhence the probe,

a sensor having a coil adapted to have a voltage induced therein by asignal generator separated from the coil by a distance,

a sensor having a circuit for powering the transmitter using an inducedvoltage.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the system environment in which thefeatures of the present invention may be implemented;

FIG. 2 is a second schematic diagram of the system environment in whichthe features of the present invention may be implemented;

FIGS. 3-5 are schematic views of various embodiments of wirelesssensor/transmitters in accordance with the invention; and

FIG. 6 is a schematic view of one embodiment of a transmitter in awireless sensor/transmitter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention may be used in connection with any wirelesssurgical navigation system for determining a position of a medicalinstrument during surgery including the method and apparatus disclosedin U.S. Pat. No. 5,592,939 to Martinelli, hereby incorporated byreference. For brevity, the details of this system, including theassembly of the coils for generating a magnetic field within ananatomical body sufficient to describe the position of a medicalinstrument and the algorithm for determining the position of the medicalinstrument, are not enclosed herein.

One aspect of the present invention relates to locating a wirelesssensor/transmitter associated with a probe, such as a catheter, insidean anatomical body. FIG. 1 illustrates an example of the invention,where the anatomical body 10 is that of a human patient undergoing asurgical or diagnostic procedure. While a human is used in this example,the invention may be used on others such as animals. In accordance withthe present invention, there is provided an apparatus for locating theposition of a wireless sensor/transmitter within an anatomical body,which apparatus includes at least one signal generator for transmittingreference signals through the anatomical body to be received by thesensor/transmitter and to be wirelessly re-transmitted by thesensor/transmitter as positional signals indicative of a location of thesensor/transmitter in the anatomical body at a given instant of time.

As embodied herein, the signal generator of the invention may include atleast one signal generator 14 which includes a coil capable ofgenerating an electromagnetic field, described more fully hereinafter.As used herein, a coil refers to an electrically conductive,magnetically sensitive element of the sensor/transmitter that isresponsive to time-varying magnetic fields for generating inducedvoltage signals as a function of, and representative of, the appliedtime-varying magnetic field. Preferably, signal generator 14 includesmultiple coils. Each coil of the signal generator 14 may be activated insuccession, each producing a magnetic field within the anatomical body10 inducing a corresponding voltage signal in a sensing coil 22 of thesensor/transmitter 12.

In the preferred embodiment of the invention, signal generator 14employs a distinct magnetic assembly so that the voltages induced in asensing coil 22 corresponding to a transmitted time-dependent magneticfield produce sufficient information to describe the location, i.e.position and orientation, of the sensor/transmitter. The signalsproduced by the signal generator containing sufficient information todescribe the position of the sensor/transmitter are referred tohereinafter as reference signals. Preferably, the reference signals arein the range of 2 KHz to 10 KHz.

In the preferred embodiment of the invention, the signal generator 14 isalso configured to induce a voltage in the sensing coil of thesensor/transmitter sufficient to power a transmitting portion of thesensor/transmitter. In the preferred embodiment, the signals transmittedby the signal generator for powering the device, hereinafter referred toas powering signals, are frequency multiplexed with the referencesignals as illustrated in FIG. 2. In the technique of frequencymultiplexing, the frequency ranges of the reference signal and poweringsignal are modulated so as to occupy mutually exclusive frequencyintervals. This technique allows the signals to be transmittedsimultaneously over a common channel, such as a wireless channel, whilekeeping the signals apart so that they do not interfere with each other.The reference and positional signals are preferably frequency modulated(FM) for a better utilization of both power and bandwidth and anincreased threshold to noise. However, amplitude modulation (AM) mayalso be used within the scope of the invention.

Alternatively, the powering signals may be transmitted by separatesignal generators, each at a differing frequencies. Preferably, thepowering signals are transmitted at higher frequencies than thereference signals. The preferred range of frequencies for the poweringsignals is 20 KHz to 200 KHz. Utilizing a higher modulation frequencythan the reference signals enables the powering signals to couple betterwith the wireless sensor/transmitter, thereby enabling a greatertransfer of power to the device. Using the preferred, mutuallyexclusive, frequency ranges for the transmission of the reference andpowering signals, enables a single coil in the wirelesssensor/transmitter to simultaneously receive both signals withoutinterference of the signals.

Also in accordance with the present invention, there is provided anapparatus for locating a wireless sensor/transmitter within ananatomical body including a receiver for receiving positional signalsfrom the wireless sensor/transmitter. As embodied herein, the receivermay include a receiver 16 that is adapted to receive radio-frequency(RF) mode positional signals or magnetic field mode positional signals.

In the preferred embodiment, the receiver 16 is adapted to receive RFsignals. The RF signals may be amplitude modulated or frequencymodulated signals in the frequency range of 1 MHz to 1 GHz. In the RFembodiment, there is no need to time multiplex the reference signalstransmitted by the signal generator with the positional signalsre-transmitted by the wireless sensor/transmitter since the signaltypes, magnetic and radio-frequency, are different. In other words,there is no concern with interference between the reference signal andthe positional signal in the RF embodiment since the receiver 16 doesnot have difficulty in separating the reference signal from thepositional signal.

However, a concern with interference between the reference signal andthe positional signal may exist if the reference signal and thepositional signal are both transmitted as a magnetic field withoutmutually exclusive frequency intervals. Therefore, in another embodimentin which the receiver is adapted to receive magnetic field modepositional signals, the transmission of the reference signals from thesignal generator 14 and the re-transmission of the positional signalsfrom the wireless sensor/transmitter 12 may be time multiplexed. Thatis, each signal may engage a wireless communication channel for only afraction of an interval on a periodic basis, so that they may jointlyutilize the common channel on a time-shared basis. In so doing, thesignals are kept apart so that they do not interfere with each other.

However, in the preferred embodiment of the receiver adapted to receivemagnetic field mode positional signals, the frequency range of thepositional signal is differed from the reference signal by avoltage-to-frequency converter within the sensor/transmitter so thattime multiplexing is unnecessary, thereby avoiding loss of cycles ofeach signal and an accompanying reduced data rate. In this case, thedevice may receive continuous powering signals and reference signalsfrom the signal generator.

Also in accordance with the present invention, there is provided anapparatus for locating a wireless sensor/transmitter within ananatomical body including a processor for computing a position of thewireless sensor/transmitter as a function of the positional signalstransmitted to the receiver. The processor may determine the position ofthe sensor/transmitter by solving equations representing signals inducedin the sensing coil in response to a sequence of magnetic fieldsgenerated successively within the anatomical body. In the preferredembodiment of the present invention, the processor begins determiningthe position of the sensor/transmitter by first determining the angularorientation of the sensing coil and then using the orientation of thecoil to further determine the position of the coil. However, aspreviously mentioned, the present invention is not limited to anyspecific method of determining the position of the wirelesssensor/transmitter.

Another function of the processor may be to electrically activate thecoil(s) of signal generator 14 to generate the desired electromagneticfields. Yet another function of the processor may be to regulate thetiming of the apparatus so that the processor may later recall whichinduced voltage corresponds to a given coil set within signal generator14 when determining a position of the sensor/transmitter.

Also in accordance with the present invention, there is provided anapparatus for locating a wireless sensor/transmitter within ananatomical body including a circuit associated with the processor foroutputting position image information to a display device. As embodiedherein, the display device may include a display device 20, such as, forexample, a CRT, LCD or other display suitable for displaying positionimage information for surgical procedures. The examples given areillustrative only. Display device 20 is not limited to any particulardisplay.

FIG. 2 provides another example of a system environment wherein receiver16, processor 18, and display device 20 are combined into anelectromagnetic control unit 32. FIG. 2 illustrates how theelectromagnetic control unit, or localizer, includes critical elementsin determining the position of a wireless sensor/transmitter.

Also in accordance with the present invention, there is provided awireless sensor/transmitter for use in surgical procedures to track themovement of structures within an anatomical body, such as organs andtissues, including a portion for receiving a reference signal from areference signal generator. The portion for receiving a reference signalincludes a coil adapted to have a voltage induced by the signalgenerator. For example, FIG. 4 illustrates a sensing coil 34 on whichthe reference signal may induce voltage corresponding to a positionalsignal indicative of a current position.

In a preferred embodiment of the invention, a sensing coil is notlimited to receiving reference signals to induce voltage correspondingto positional signals. Instead, the sensing coil may also receivepowering signals which induce sufficient voltage to power thetransmitter. In the preferred embodiment of the device illustrated inFIGS. 2 and 3, sensing coil/power coil 22 induces voltage correspondingto both reference and positional signals from signal generator 14.

As embodied herein, the portion for receiving a reference signal furtherincludes a sensing unit and a powering circuit, such as sensing unit 24and power circuit 26 shown in FIGS. 2 and 3. Sensing unit 24 and powercircuit 26 of the preferred embodiment each may receive an inducedvoltage signal due to a frequency multiplexed reference signal andpowering signal on sensing/powering coil 22. Sensing unit 24 andpowering circuit 26 both may separate the voltage signals induced by themultiplexed magnetic signals into positional and powering signals.Standard frequency demodulating techniques are used for separating thesignals.

Upon separation of the positional and powering signals, sensing unit 24may measure the induced voltage signal portion corresponding to areference signal as a positional signal indicative of a current positionof a wireless sensor/transmitter 12. The positional signal is retainedfor further processing and re-transmission by a transmitting portion ofthe sensor/transmitter. Similarly, power circuit 26 may retain theinduced voltage signal portion corresponding to a powering signal foruse by the power circuit in producing power. Powering circuit 26 mayrectify the induced voltage generated on a coil by the powering signalsto produce DC power. Powering circuit 28 may store the DC power using acapacitor, small battery, or other storage means for later use by one ormore components of the wireless sensor/transmitter. In a preferredembodiment, the DC power is produced continuously by powering circuit 26and storage is not necessary.

In another embodiment shown in FIG. 4, separate coils are used forreceiving, respectively, the reference signals and the powering signals.The processing performed by sensing unit 26 and power circuit 26 on theinduced voltage signals corresponding to a frequency multiplexedreference signal and powering signal remain unchanged. Due to spaceconstraints of the wireless sensor/transmitter, the aforementionedembodiment which utilizes a single coil in the system for powering thetransmitter is preferred.

Also in accordance with the present invention, there is provided awireless sensor/transmitter for use in surgical procedures to track themovement of structures within an anatomical body including a portion forwirelessly transmitting the reference signal as a positional signalindicative of a current position of the sensor. As illustrated in FIG.2, the transmitting portion may include a transmission processing unit27 that processes positional signals for transmission and then transmitsthe positional signals to a receiver.

Transmission processing unit 27 may include a voltage-to-frequencyconverter, embodied herein as voltage-to-frequency converter 28.Voltage-to-frequency converter converts the induced voltage signalcorresponding to the position of a wireless sensor/transmitter to acorresponding signal with a transmission frequency which is proportionalto the measured voltage. The frequencies produced by the converter maybe made to vary within a given range. Preferably, voltage-to-frequencyconverter 28 is powered by the rectifier circuit of power circuit 26. Inother embodiments, however, a battery or other power source may powervoltage-to-frequency converter 28.

Transmission processing unit 27 also may include a transmitter, embodiedherein as transmitter 30. Transmitter 30, and hence transmissionprocessing unit 27, may be configured for RF transmission or magneticfield transmission.

If RF transmission is employed, transmitter 30 may include an antenna toretransmit the positional signal to a receiver. The positional signal ispreferably transmitted by the sensor/transmitter in the frequency rangeof 1 MHz to 1 GHz, where voltage-to-frequency converter 28 is adapted toproduce the positional signal in the given frequency range according tothe measured induced voltage. In the RF embodiment, as previouslymentioned, transmitter 30 does not need to time-multiplex there-transmission of positional signals with the transmission of referencesignals since no interference between the signals occurs.

If magnetic field transmission is employed, transmitter 30 may include acoil arrangement to transmit the positional signal to the receiver.Transmitter 30 may have its own magnetic coil or it may share the coilof the sensing unit. As shown in FIG. 5, the transmitter may share acoil 38 that is used by both sensing unit 24 and power circuit 26. Thepositional signal is preferably transmitted by the sensor/transmitter inthe frequency range of 50 KHz to 200 KHz. Using voltage-to-frequencyconverter 28 to produce the positional signal in the preferred frequencyrange according to the measured induced voltage, the system maymultiplex the transmitted reference signal and re-transmitted positionalsignal in frequency, rather than in time. While another embodiment maybe to time multiplex the reference and positional signals duringmagnetic field transmission, frequency multiplexing is preferred as itallows both signals to be transmitted simultaneously.

Alternatively, the transmitting portion of the wirelesssensor/transmitter may include an inductor-capacitor (LC) tank circuitinstead of a coil to transmit the positional signal via a magnetic fieldmode to the receiver. If an LC tank circuit is used instead of a coilfor magnetic transmission of the positional signal, the LC tank circuitis tuned to a resonant frequency to receive the magnetic field andtransmit it to the wireless magnetic receiver. As stated above, theposition signal may have its frequencies changed from those of thereference signal to avoid time multiplexing during transmission, or itmay use time multiplexing for simplification of the processing andtransmission of the positional signal upon receiving the same.

The transmitting portion may also transmit the positional signal viadigital RF transmission. If digital RF transmission is chosen, thetransmission processing unit 27 may include an analog-to-digital (A/D)converter for converting the analog signal to digital. The A/D convertermay include an A/D converter 40 shown in FIG. 6. The A/D converter 40may be interfaced to a signal transmission module for directtransmission after conversion, or it may be interfaced to a digitalsignal processor (DSP) system for further processing.

In a preferred embodiment illustrated in FIG. 6, the transmissionprocessing unit further includes a DSP system 42. A DSP system allowsfor more effective use of the transmission bandwidth by processing thepositional signal using conventional coding and compression techniques.The DSP system may be interfaced to a signal transmission module 44.Signal transmission module 44 of the present invention uses techniquessimilar to wireless modems or digital RF techniques to transmit thesignal to the wireless receiver. In another embodiment, the DSP may beintegrated with the A/D converter to conserve space. The A/D converter,DSP, and signal transmission module are preferably powered by powercircuit 26. However, one or more of the above devices may be powered bya battery or other power source.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. For example, instead of using the inducedvoltage on the sensing coil to find the position of a wirelesssensor/transmitter, one could induce voltage on a sensing coil of aprobe to power any sensor or battery in the anatomical body. One sensorreceiving power, for example, may be a thermostat for measuringtemperature within the chamber of the heart.

Another embodiment of the invention may derive power in a wirelesssensor/transmitter through an optical means. For example, the power coilof the present invention could be substituted with a photocell or solarcell to obtain optical power from an optical transmitter, such asinfrared or a light-emitting diode (LED), and convert it to electricalpower for use by the device. Moreover, any transmitter in the system maybe substituted with an optical transmission means. Optical transmissionmeans may be combined with other transmission means, such as magnetic orRF transmissions. For example, the sensing coil may receiveelectromagnetic signals for powering transmitter 30, while transmitter30 may generate optical signals to receiver 16. The present inventionallows various types of transmission

It is intended that the specification and examples be considered asexemplary only, with a true scope and spirit of the invention beingindicated by the following claims.

What is claimed is:
 1. A surgical navigation apparatus for locating awireless sensor/transmitter within an anatomical body during a surgicalprocedure, the apparatus comprising: at least one signal generatorremote from the anatomical body for sending reference signals throughthe anatomical body to be received by the sensor/transmitter and to bewirelessly re-transmitted by the sensor/transmitter as positionalsignals indicative of a current location of the sensor/transmitterwithin the anatomical body; a receiver for receiving positional signalsfrom the wireless sensor/transmitter; a processor for computing aposition of the wireless sensor/transmitter as a function of thepositional signals transmitted to the receiver; and a circuit associatedwith the processor for outputting position image information to adisplay device.
 2. The apparatus of claim 1, wherein the said at leastone signal generator includes an electromagnetic field generator coil.3. The apparatus of claim 2, wherein the sensor/transmitter includes asensing coil and wherein the signal generator is configured to induce avoltage in the sensing coil sufficient to power a transmitting portionof the sensor/transmitter.
 4. The apparatus of claim 1, wherein thereceiver is adapted to receive RF mode positional signals transmitted bythe sensor/transmitter.
 5. The apparatus of claim 1, wherein thereceiver is adapted to receive digital RF mode positional signalstransmitted by the sensor/transmitter.
 6. The apparatus of claim 1,wherein the receiver is adapted to receive magnetic field modepositional signals transmitted by the sensor/transmitter.
 7. A wirelesssensor/transmitter for use in surgical procedures to track the movementof structures within an anatomical body, comprising: a portion forreceiving a reference signal from a reference signal generator that isremote from the anatomical body; and a portion for wirelesslytransmitting the reference signal as a positional signal indicative of acurrent position of the sensor.
 8. The wireless sensor/transmitter ofclaim 7, wherein the receiving portion includes a coil adapted to have avoltage induced by the signal generator.
 9. The wirelesssensor/transmitter of claim 8 further including a circuit for poweringthe transmitter using the induced voltage.
 10. The wirelesssensor/transmitter of claim 7, wherein the transmitting portion includesa voltage to frequency converter.
 11. The wireless sensor/transmitter ofclaim 10, wherein the transmitting portion further includes an antenna.12. The wireless sensor/transmitter of claim 10, wherein thetransmitting portion further includes a coil.
 13. The wirelesssensor/transmitter of claim 7, wherein the transmitting portion includesan A/D converter and a signal transmission module.
 14. The wirelesssensor/transmitter of claim 10, wherein the transmitting portionincludes an LC tank circuit.
 15. The wireless sensor/transmitter ofclaim 13, wherein the transmitting portion further includes a DSP forprocessing and compressing the positional signal to be transmitted. 16.A surgical navigation apparatus for navigating a surgical instrumentwithin an anatomical body during a surgical procedure, said surgicalnavigation apparatus comprising: a signal generator operable to transmitreference signals into the anatomical body from a site remote from theanatomical body; and a wireless sensor/transmitter attached to thesurgical instrument, said wireless sensor/transmitter operable toreceive said reference signals from said signal generator and operableto wirelessly transmit position signals indicative of a current locationof the surgical instrument during the surgical procedure.
 17. Thesurgical navigation apparatus as defined in claim 16 wherein saidwireless sensor/transmitter further includes a coil operable to receivea signal from said signal generator to induce a voltage sufficient topower said wireless sensor/transmitter.
 18. The surgical navigationapparatus as defined in claim 17 wherein said coil is both a sensingcoil operable to sense said reference signals from said signal generatorand a power coil operable to generate a voltage sufficient to power saidwireless sensor/transmitter.
 19. The surgical navigation apparatus asdefined in claim 1 wherein said sensor/transmitter is attached to asurgical instrument.
 20. The wireless sensor/transmitter as defined inclaim 7 wherein said wireless sensor/transmitter is attached to asurgical instrument.